Hydraulic transmission system



Sept. 25, 1945. A. H. HOPMANS HYDRAULIC TRANSMISSION SYSTEM Filed Dec. 18, 1945 2 Sheets-Sheet l Q FIG: .5.

. INVENTOR. A07 eHHp/m/w,

Sept. 25; 1945. v A. H. HOPMANS 2,385,625

- HYDRAULIC TRANSMISSION SYSTEM 7 Filed Dec. 18, 1943 2 Sheets-Sheet 2 %Mmm,7/AJU1/m in MIMI llll'lll Ill! /71 V f MM IN VEN TOR. I A ens 02H. HOP/11416,

Patented Sept. 25, 1945 Arthur H. Hopmans, Paulding, Ohio Application December 18, 1943, Serial No. 514,763

1 Claim.

My invention relates to a hydraulic power transmission system and has particular reference to a control device for use in hydraulic systems such as hydraulic brakes for automobiles and hydraulically operated clamps and workholding devices, and finds particular utility when employed to maintain the fluid system completely filled with fluid at all times or, alternatively, to maintain a predetermined minimum pressure in the system.

In certain hydraulic power systems, notably the power transmission systems used in hydraulic brakes on automobiles and trucks, the length of stroke required of the driving element or master piston increases astime goes on as a result of the gradual'loss of fluid from the system and the wearing away of the brake lining. This condition gradually gets worse and worse until eventually it becomes necessary to readjust the mechanical part of the system as by changing the location of the return stops for the brake shoes in order to insure an adequate travel of the master cylinder. ,Because of the gradually growing magnitude, of the condition referred to, it is not unusual for the readjustment of the system to be postponed until after the system is incapable of developing the braking effort required for safe operation of the vehicle.

specifications, read in connection with the accompanying drawings, wherein:

Fig. 1 is a diagrammatic view illustrating the manner in which the system of my invention is used when employed as the operating system for hydraulic brakes on an hicle;

Fig. 2 is a longitudinal sectional view through a check valve mechanism forming a part of the system shown in Fig. 1 and showing the parts in the positions they normally, occupy when no braking eflort is being developed:

Fig. 3 is a view similar to Fig; 2 but illustrating the relative positions of the parts when the automobile or other vebrakes are applied;

Fig. 4 is a cross sectional view taken suihstan tially along the line IV-IV of Fig. 2;

Fig. 5 is a longitudinal sectional view of a modifled term of check valve arrangement winch may The present invention is directed to a mecha- Q nism' which may be used in hydraulic brake systems and like hydraulic power transmission systems for the purpose of maintaining, altematively, a given amount of fluid in the system or a given minimum pressure in the system.

It is therefore an object of the present invention to provide a hydraulic power transmission system which overcomes the disadvantages above referred to by including between the driving element and the driven element a check valve constructedand arranged to permit a limited returnflow of fluid.

It is also an object of my invention to provide a system of the character referred to in the preceding paragraph in which the check valve is carried in a piston which is in turn mounted for limited movement within a cylinder.

It is an additional object of my invention to provide a system of the character set forth in the preceding paragraphs in which the piston provides a differential area'and is continuously urged in one direction as by means of a spring to thereby maintain within the system a predetermined operating pressure. 1

Other objects and advantages of my invention will be apparent from a study of the following parts during the time br s r:

be used with the systems shown in Fig. '1 and which is arranged to maintain the predetermined .n i u. operating pressure in the system, the parts in Fig. 5 being shown in the positions they normally occupy when no braking short is being developed;

Fig. 6 is a view similar to Fig. 5 but illustrating the relative positions occupied by the parts when the slack or play is taken out of the brakes or driven elements of the system;

Fig. 7 is a view similar to Figs. 5 and 6' but showing the relative positions occupied by the eflort is being developed by the hydraulic brakes; and

Fig. 8 is a cross sectional view taken substantially along the line VIII-VH1 of Fig. 5.

Referringto the drawings. I have illustrated in shown) and constituting the driving element for the system. The master cylinder I and its pistons are, in the conventional manner, operatively connected to a brake pedal 2 as by means of a rod 3.

Upon depression of the brake pedal 2 fluid is discharged from the cylinder I and conveyed by means of conduits l, 5 and 6 to the front or dirigible wheels I and l of the vehicle whereat the fluid pressure is applied to driven elements or wheel cylinders 9 and Ill These cylinders are, in

the conventional manner, equipped with opposed pistons arranged to be moved in oppositedirections upon the application of fluid pressure to the-cylinders to thereby expand brake shoes (not shown) into frictional braking engagement with front wheel brake drums H- and I2. At the same Each of the elements 22 is identical and it is therefore concluded that a description of the element 22 associated with the left front wheell will be a sufilcient description or all of the devices 22. The device referred to is shown 'in detail in Fig. 2 and includes a body or cylinder member 23 provided at one end with means 24 for attach- 625 fluid from the wheel cylinder I is arrested and the brake shoes are then held in a corresponding 4 movement of the brake shoes is permitted than ment to the wheel cylinders l0 and similar means i at the opposite end for attachment to the line 8.

The body member 22 is bored interiorly to dey fine a cylinder bore 26 within which is slidably mounted a piston 21. The cylinder 23 communicates with an. inlet bore 28 through which fluid is supplied from the line 6. The piston 21 constitutes a check valve housing and is accordingly interiorly bored as shown at 29 toreceive a ball valve member which-is spring urged against a valve seat 3| to close an inlet port 32, a compression spring '33 being confined between the ball 30 and a threaded retainer ring 34 preferably screwed into the outer end of the bore 29.

I have shown in Fig. 2' the relative positions occupied by the described parts when the system is idle and no braking effort is being developed.

was permitted in the first instance. However, as the brakes are applied from time to time, the brake lining material will be gradually worn away so that upon each new application of the brakes a small quantity of fluid will move past the che'ckvalve 30 so that the normal retracted position of the brake shoes will be continually advanced at the same rate as the brake lining is worn'away. This insures that-there will at all times be made available an adequate strokeof ,the master piston to insure the development of full braking efl'ort.

It will be seen thatthe parts must be so adjusted that the permissible movement of the piston 21 will be at least sufiicient to pass to the wheel cylinder in that amount of fluid which is required to, move the brake shoes from a position just clear of the brake drums to a position corresponding to the development of maximum braking effort. If less movement of the piston When the brakes'are applied by the depression of the brake pedal 2, the piston 21 is slid to the left as viewed in Fig. 2 to a position such as that shown in Fig. 3 as a result of the flow oi fluid into the cylinder bore 26' through the inlet bore 23.

- The motion of the piston 21 is arrested in a position shown in Fig. 3 by the engagement of the piston with the end of the fitting which is'screwed into the threads 24.

Until this engagement is obtained, the check valve 30 remains closed as shownin Fig. 2 since .there is no pressure differential available to open the valve. However, when the piston 21 is arrested and additional pressure is applied at the inlet bore 28 as a result or further depression of 21 were to be permitted, depression of the brake pedal would shift the normal retracted position of the shoes outwardly a distance sufiicient to cause the brakes to drag.

I have shown in Figs. 5 through 8 a modified form of control element 22, the form in these the brake pedal 2, the check valve 30 will open to a position such as that shown in Fig. 3 to permit additional fluid to pass through the port 32 around the ball 30 and through the interior bore 29, thus applying additional pressure to the brake cylinder it and further separating the two pistons con= tamed therein.

when the brakes are released as by removing the force which has been applied to the brake pedal 2, the brake shoe springs which are included in the usual braking mechanism and. which tend to withdraw the shoes from engagement with the brake drum I2 will cause a return how of fluid from the brake cylinder it into the bore 2e, thus causing the return of the piston 2'! from the position shown in Fig. 3 to the position shown in Fig.

'2, it being realized that the check valve 38 is moved to its closed position such as is shown in Fig. 2 immediately upon the equalization of the pressure between the inlet bore 28 and the cylinder bore 26-. 3

As soon as the piston 21 arrives at its initial position which is shown in Fig. 2, further flow of figures being arranged to provide at the wheel cylinders an increased operating pressure.

The form of the invention which is shown in Figs. 5 through 8 comprises a cylinder body which is bored internally to define a cylinder bore 33 withinvwhich is slidably mounted a piston 31 carrying a piston ring or plunger washer 38. The

cylinder 35 .is provided with an integral inlet I closure 39 which is provided with means 40 for attachment to the conduit 8. The opposite end of the cylinder at is preferably closed as by means of a closure plate as which is provided with means $2 for attachment to the wheel cylinder Ill. The closure it also carries an inwardly extending boss 53 which is bored as indicated at id to define a cylinder bore within which is received a reduced diameter portion d5 of the piston 31, an adequate seal between the portion and the cylinder bore t l being obtained by as by means of a cup washer as.

The cup washer dd is bored as indicated at All to provide a fluid interconnection between the cylinder here as and an internal bore or interior cylinder 3d of the piston portion 55.

Within the bore 4% is slidably mounted a check valve carrier d9 which is bored as indicated at so to receive a ball check valve 5i normally urged to the right as shown in Fig. 5 as by means of a spring 52 into engagement with a ball valve seat defined by the bore and a small diameter bore 53. The spring 22 is confined between the ball 51 and a collar 56 threaded into theleit-hand end of the bore lid. The inner cylinder bore 68 is provided. with a reduced diameter'continuation which communicates with theright-hand end of the piston 31. The piston 31 is normally urged tothcrig'htasshowninFig.5bymeansofa compression spring 50 which is conflned between the piston I1 and the closure plate 4|. A bleeder hole It may be provided through the wall of the cylinder 35 to permit air to be exhausted upon movement of the piston 31 to the left as shown in Fig. 5.

With th apparatus just described, depression of the brake pedal will force fluid into the interior of the cylinder housing 35 through the inlet l. at the right-hand end of the piston 31. This fluid will be conducted through the bore 55 and will result in the check valve carrier 49 being from its seat and to permit fluid to flow through the openings 53 and ill to supply additional fluid to the wheel cylinder l0. It will be recognized that during this phase of the operation, the compression spring 58 has served 'to hold the piston I! in its right-hand position as shown in Figs. 5 and 6. As soon, however, as the brake shoes are engaged with the brake drum, a back pressure is developed to cause a substantial pressure rise within the bore 44 and within the bore 38 to the right of the piston TI. This applies an equal pressure to the piston portion 45 and to the piston portion 31 but because of the larger area of the portion 31, there will be developed a resultant force tending to urge the piston 31 to the left against the force of the spring 56. when this resultant force rises to a value sufllcient to overcome the force of the spring lit, the piston 31 will move to the left toward a position such as that shown in Fig. 7.

I As the piston 31 moves to the left, the fluid displaced from the chamber 44 will flow through the passage 41 to force the check valve carrier 40 to its furthest right-hand position as shown in Fig. 7. Thereafter the increase in pressure within her it of a fluid pressure which is greater than that exerted on the piston 31, the magnitude of is balanced by the force developed on the piston I! which is equal to the differential area times the differential pressure in the system, the.

apparatus will operate to apply to the wheel cylinder Ill an operating pressure substantially greater than the pressure developed by the master cylinder I. Also assuming that in the first instance some fluid is moved past .the ball check 5|, the amount of fluid returned to the master cylinder from the brake cylinder will be less than the amount previously moved in the, opposite 7 but as the brake lining wears away in response ,to repeated operation of the brakes, an additional small amount of fluid will be injected past the check valve 5| upon each operation of the brakes so that the brake shoes are always held, when released, at a position just clearing the brake drum.

From the foregoing it will be observed that I-have provided a hydraulic power transmission system which is characterized by providing control members for permitting only a limited return flow of fluid from the driven elements to the driving element. Thus, in the case of a hydraulic braking system for automobiles or other vehicles,

. the wear in the brake linings is automatically the pressure in the cylinder 44 with respect to that applied to the piston 31 being proportional to the relative areas of the piston 31 and the small piston portion 48.

Upon releaseof pressure from the brake pedal 2, the resulting drop in pressure will permit the spring so to start moving the piston 31 to the right toward the position illustrated in Fig. -5. At the same time the check valve BI is held closed by the spring 5!- so that the fluid returned from Fluid flow from the wheelcylinder It will be arrested at the time the piston 31 reaches its extreme right-hand .position as shown in Fig. 5."

It will be seen that since the force of the spring ing.

taken up by the control devices so that a maximum efiective pedal stroke is maintained at all times without requiring period adjustment of the brake shoe stops.

It will also be observed that I have illustratec a modified type of control device which in addition to controlling the amount of return movement of the driven element as in the first described modiflcation, operates to provide a much greater operating pressure than is produced by the master cylinder.

While I have shown and described the preferred embodiment of my invention, I do not desire.

.to be limited to any of the details of construction shown or described herein, except as defined in the appended claim.

I'claim:

mission systems, the combination of: a, cylinder housing defining a cylinder bore having a large diameter portion and a small diameter portion;

means closing each end of said cylinder housing and providing connection to fluid conduits; a piston reciprocal'in said bore having a large diameter portion and a small diameter portion fitted respectively into said large and small diameter bore portions, said piston having a fluid passage extended axially therethrough; a tubular valve carrier slidably mounted in said passage and having an opening extending longitudinally therethrough; a check valve. on said carrier normally closing said opening to positively .prevent flow of fluid from said small diameter bore portion toward said large diameter bore portion; and spring means normally urging said piston toward the large diameter bore portion of said cylinder houssa'rmla n. HOPMANS.

In a control device for hydraulic power trans- 

